It is conventional to provide a maintenance station for ink-jet printers, the maintenance station including a wiper for wiping the nozzle plate of the printhead cartridge and a cap for providing a sealed environment around the ink-jet nozzles to prevent ink from drying in the nozzles during periods of non-use.
The cap is a cup-shaped elastomeric member which is brought into contact with a nozzle plate/chip/tab circuit assembly on the cartridge to accomplish capping. As the cap is moved into contact with the cartridge, air may be trapped between the cap and the cartridge and forced through the nozzles and into adjacent ink feed channels through which ink is supplied to the nozzles. Ink is normally sucked through the feed channels by the firing of the nozzles hence the forcing of air into the feed channels can lead to a loss of prime and degraded performance of the cartridge.
A further problem may be encountered as the cartridge is uncapped. If the cup has formed an air-tight seal against the cartridge, then as the cup is moved away from the cartridge a vacuum may be created in the sealed region thus drawing ink out of the ink feed channels. This depletes the ink supply and thus shortens the useful life of the cartridge. Furthermore, the excess ink contaminates the region of the printer where the maintenance station is located.
Various means are known for relieving the pressure at the nozzles as the cartridge is capped or uncapped. U.S. Pat. No. 5,155,479 provides a cap with notches in the edges of the cap that contact the cartridge, the notches serving as passages through which air may flow from the sealed region to the surrounding environment. However, the maintenance station region is prone to contamination due to planned ink spitting, and air flow passages provided in or on the cap may become clogged or blocked. Furthermore, a given printer may use different cartridges some of which might require different controlled levels of venting.